1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member having an undercoat layer, a process for producing the electrophotographic photosensitive member, and to titanium oxide which is surface-treated so as to impart hydrophobicity thereto.
2. Description of the Background
In recent years, electrophotographic techniques have been extensively applied to not only copying machines but also various printers, because of, for example, high printing speed and formation of high-quality images. As photosensitive members constituting the main component of electrophotographic apparatuses, organic photoconductive materials (OPC) have become predominately used instead of inorganic photoconductive materials, such as selenium, arsenic-selenium alloy, cadmium sulfide or zinc oxide, because of the ease in selection of exposure light wavelength range, facilitated production producible by coating), use of harmless materials from the standpoint of safety, among others. There have been developed various type OPCs such as single layer type OPCs obtained by dispersing a charge-generation substance and a charge-transport substance in a binder, laminated type OPCs comprising two function-separating layers, i.e., a charge-generation layer and a charge-transport layer, and the like. Among these OPCs, the laminated-type OPCs having such a structure that the charge-generation layer and the charge-transport layer are successively laminated on a substrate, have been ordinarily used.
Further, recently, in order to enhance electrophotographic properties, image-forming properties and mechanical properties of the photosensitive member, electrophotographic photosensitive members obtained by successively laminating an undercoat layer and a photosensitive layer on a substrate have been widely used.
As preferable binder resins for the undercoat layer, there have been studied and frequently used alcohol-soluble resins, especially alcohol-soluble polyaride resins, from the standpoints of adhesion to the substrate, solvent resistance (resistance to solvents used in the charge-generation and charge-transport layers), coating property and electric barrier property.
Further, in order to satisfy the requirements for the undercoat layer, inorganic particles such as metal oxide particles, especially titanium oxide particles, have been used in the undercoat layer. Besides, in order to enhance the performance of the undercoat layer, there has been developed such a technique that the metal oxide particles are treated with an organic compound. In particular, there is known a method of treating the particles with a metal-containing organic compound such as an organic silicon compound (U.S. Pat. No. 5,612,158).
As metal oxide particles treated with such an organic compound, there is ordinarily known those treated with polysiloxanes such as dimethyl polysiloxane or methyl hydrogen polysiloxane, stearic acid or the like.
Meanwhile, when a coating solution containing metal oxide particles treated with an organic compound is prepared, the organic compound is usually liberated in the coating solution upon dispersion- and heat-treatments or the like. In addition, after the production of the coating solution, the organic compound is liberated over time. At present, it has been difficult to completely prevent the liberation of the organic compound as a treating agent.
For this reason, in the case where the layer containing metal oxide particles treated with an organic compound, is formed by coating, the organic compound liberated from the metal oxide particles tends to be associated with each other in the coating solution, so that defects such as crawling tend to occur upon coating. As a result, a good coating film is difficult to produce. Especially in the case of electrophotographic photosensitive members, the defects, such as crawling in the undercoat layer tend to cause image defects, resulting in problems such as deteriorated yield.
In order to solve these problems, there has been proposed, for example, a method of preventing an organic compound from being liberated in a coating solution by previously washing the organic compound-treated metal oxide particles with an organic solvent, thereby inhibiting defects such as crawling of the undercoat layer (Japanese Patent Application Laid-open (KOKAI) No. 10-282502).
However, this method requires additional steps such as washing with the organic solvent, separating between the organic solvent and the metal oxide particles, drying of the metal oxide particles or the like. As a result, the method becomes disadvantageous in productivity and costs.
Accordingly, there remains a need for electrophotographic photosensitive members which overcome the disadvantages described above.